It is commonly accepted that at least minimal physical activity is necessary to maintain muscle mass. If such minimal activity is lacking, the muscular system becomes atrophied and muscle mass diminishes. Muscular activity is energetically consuming, i.e. oxygen consumption by the muscular system increases heavily during physical activity. For example, oxygen consumption for a healthy person at rest may increase 10–15 times with physical activity. If an adequate amount of oxygen fails to reach the muscle, physical activity will be limited. Inadequate oxygen delivery may be due to a disorder in oxygen reception in the lungs or to insufficient transport of the oxygen to the muscles. Insufficient pumping of the heart is designated heart insufficiency. Muscle reduction begins in those with heart disease as a result of insufficient activation of the heart muscles. This in turn leads to a further reduction of the pumping performance of the heart thereby resulting in circulus vitiosus. The present invention can be used to interrupt this process or condition.
Stength gains occur when muscle produces force. If the muscle shortens while producing force, it produces concentric (Con) positive work. If it lengthens while producing force, work is done on the muscle resulting in eccentric (Ecc) negative work. A muscle action is designated “concentric” if the force of a muscle overcomes an applied resistance and a muscle action is designated “eccentric” if the muscle force is less than the applied resistance. “Acceleration work” results from concentric contractions and “deceleration work” results from eccentric contractions. For example, one may imagine that ascending a mountain requires exclusively concentric work and that descending the same mountain requires mostly only eccentric work. From a physical point of view, equal energy is converted in both cases. In ascending, potential energy is gained while in descending, the same amount of energy is lost. Although physically the same energy amounts are converted, the amount of energy to be spent by the muscular system for ascending is much higher than the amount of energy lost in descending. Five to seven times more energy is spent for concentric work as is spent for physically equal eccentric work.
The magnitude of strength gains seems to be a function of the magnitude of the force produced regardless of its Ecc or Con work. Ecc training has the capability of “overloading” the muscle to a greater extent than Con training because much greater force can be produced eccentrically than concentrically. Accordingly, Ecc training can result in greater increases in strength.
Furthermore, the Ecc mode of contraction has another unique attribute. The metabolic cost required to produce force is greatly reduced; muscles contracting eccentrically get “more for less” as they attain high muscle tensions at low metabolic costs. In other words, Ecc contractions cannot only produce the highest forces in muscle vs. Con or isometric contractions, but do so at a greatly reduced oxygen requirement (Vo2). This observation has been well-documented since the pioneering work of Bigland-Ritchie and Woods (Integrated eletromyogram and oxygen uptake during positive and negative work, Journal of Physiology (Lond) 260:267–277, 1976) who reported that the oxygen requirement of submaximal Ecc cycling is only 1/6–1/7 of that for Con cycling at the same workload Typically, single bouts of Ecc exercise at high work rates (200–250 W for 30–45 minutes) result in muscle soreness, weakness, and damage in untrained subjects. Therefore, the common perception remains that Ecc muscle contractions necessarily cause muscle pain and injury. Perhaps because of this established association between Ecc contractions and muscle injury, few studies have examined prolonged exposure to Ecc training and its effect on muscle injury and strength. Nonetheless, Ecc contractions abound in normal activities such as walking, jogging, descending/walking down any incline, or lowering oneself into a chair to name just a few. Obviously, these activities occur in the absence of any muscular damage or injury.
Accordingly, there is a need for providing chronic Ecc training techniques and/or apparatus that can improve locomotor muscle strength without causing muscle injury.